Canvas HTML5. Случайные линии

var canvas = document.getElementById("canvas"); 
var ctx = canvas.getContext("2d"); 
 
function createRandomLine() { 
  var beginRandX = Math.floor(Math.random() * canvas.width); 
  var beginRandY = Math.floor(Math.random() * canvas.height); 
  var endRandX = Math.floor(Math.random() * canvas.width); 
  var endRandY = Math.floor(Math.random() * canvas.height); 
 
  ctx.beginPath(); 
  ctx.moveTo(beginRandX, beginRandY); 
  ctx.lineTo(endRandX, endRandY); 
  ctx.closePath(); 
  ctx.strokeStyle = "red"; 
  ctx.lineWidth = 3; 
  ctx.stroke(); 
}

canvas { 
  border: 1px solid black; 
  width:300px; 
  height:200px; 
}

<canvas id="canvas" onclick="createRandomLine()"></canvas>